1. Field of the Invention
The present invention relates to a snap fastener with tape, which is made of synthetic resin, and a manufacturing method and a mold of the snap fastener.
2. Description of the Related Art
It has been known for a long time to form at least one attachment hole in a single tape, and integrally mold an eyelet or a similar article made of synthetic resin with a desired shape onto front and back faces of the tape such that the eyelet or the article holds a peripheral edge of the attachment hole. As disclosed in U.S. Pat. No. 2,821,764, for example, an attachment hole is formed in a sheet material, and an eyelet made of synthetic resin with a desired shape is integrally molded on front and back faces of the sheet material so as to hold a peripheral edge of the attachment hole. The eyelet is molded as such by clamping the sheet material extending in an annular cavity for molding the eyelet, at a plurality positions at the peripheral edge portion of the attachment hole as a center, by using a plurality of pairs of pin members projecting in the cavity so as to face each other, and by introducing molten resin into the cavity.
In general, if the pin members do not exist in the above-described molding, the peripheral edge of the attachment hole of the sheet material extending in the cavity largely waves in a peripheral direction due to an introducing pressure of the molten resin. At worst, a portion of the peripheral edge may be deflected so as to abut on an inner face of the cavity, so that the sheet material may be exposed at a portion of a surface of the eyelet as a molded product. The invention disclosed in the above U.S. patent has been accomplished by taking notice of that a proper degree of waving of the peripheral edge of the attachment hole in the sheet material increases a strength of securing of the eyelet to the sheet material. In order to obtain the proper degree of waving state, the peripheral edge portion of the attachment hole of the sheet material is clamped by the pin members in the cavity, thereby controlling a degree of the waving.
There is a similar invention that follows the above technical idea of preventing excessive waving, which is as disclosed in European Patent No. 0228293. In the European patent, a fastener member of a snap fastener, not limited to a male button or a female button and including the above-described eyelet, is integrally molded on a tape by a method similar to that in the above U.S. patent.
In the above U.S. patent, however, an inlet for introducing the molten resin into the cavity is formed so as to face the peripheral edge of the attachment hole so that the molten resin introduced into the cavity by injection can smoothly flow to the front and back faces of the attachment hole of the sheet material. In other words, the molten resin introduced from a center of the annular cavity is guided toward an outer diameter in a plane including the attachment hole. The molten resin supplied from the inlet is forwarded respectively to the front and back faces of the sheet material at the peripheral edge of the attachment hole. With this structure, because the sheet material is incorporated with the eyelet at the peripheral edge of the attachment hole in a proper degree of waving state, the securing strength increases.
According to the above invention, however, a thin disk-shaped plate made of synthetic resin is integrally molded at a central opening portion of the molded eyelet, so that a peripheral face of the opening portion of the molded eyelet must be trimmed after removing the thin plate after molding as described in the specification.
In the European patent, on the other hand, because a specific molding method is not disclosed, unlike the above-described U.S. patent, it is unclear how the molten resin is introduced into the cavity. However, according to FIG. 4 showing its representative embodiment, it is apparent that the molten resin is not introduced into the cavity from a portion for forming and the engaging opening of a female member, because upper and lower molds for forming the engaging opening contact with each other at a parting line thereof. Therefore, the European patent is considered to be different from the U.S. patent in this point. However, if an inlet for introducing molten resin communicating with the cavity is formed at a position other than an inner peripheral engaging face of the opening, e.g., a portion adjacent to the pin member on a side for forming the opening, an resin introducing pressure is locally and directly applied to one side of the peripheral edge of the attachment hole of the tape at the beginning of introduction of the molten resin, and thus, a waving phenomenon is liable to be generated.
In order to prevent this moving phenomenon, eight pin members are provided for clamping the tape at positions close to the peripheral edge portion of the attachment hole. Because of this structure, the molds are complicated and the resin flows from one face of the tape to the other face. Thus, a setting of molding conditions for preventing an influence of the flowing of the resin is complicated.